I bought a Hawke Vantage 3-9x40ao, and it is too long to be mounted on a Swarm Bone Collector Gen2; the cocking will knock the magazine holder against the front of the scope. Rookie mistake on my part: I mounted without the top bolt so that that scope can be moved back a little. That didn't work out too well. It damaged the scope rail after about 30 rounds. I'm looking at other mounting options now, the Bullseye being one of those options.